Flexible display device and method for manufacturing thereof

ABSTRACT

The present disclosure provides a method for manufacturing the flexible display device. The method for manufacturing the flexible display device includes the following steps. First, a flexible substrate and a bonding structure are provided, in which the bonding structure is disposed on the flexible substrate. Subsequently, an anisotropic conductive film is provided on the bonding structure. Then, a driving circuit is provided on the anisotropic conductive film. Thereafter, the anisotropic conductive film is cured at a bonding temperature greater than or equal to 140° C. and less than or equal to 165° C.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 17/099,805,filed on Nov. 17, 2020. The content of the application is incorporatedherein by reference.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates to a method for manufacturing theflexible display device, and more particularly to a method formanufacturing a flexible display device having a flexible substrate.

2. Description of the Prior Art

Flexible display devices are widely used in daily life, and displaypanels of the flexible display devices may be driven by integratedcircuit chips and flexible circuit boards. Therefore, how to improve aquality of electrical connections between the integrated circuit chipsand the display panels or between the flexible circuit boards and thedisplay panels in the flexible display device or a display quality or areliability of the flexible display device is one of many topicsrequired for discussion and further research in the field.

SUMMARY OF THE DISCLOSURE

According to an embodiment of the present disclosure, a method formanufacturing a flexible display device is provided. First, a flexiblesubstrate and a bonding structure are provided, wherein the bondingstructure is disposed on the flexible substrate. Subsequently, ananisotropic conductive film is provided on the bonding structure. Next,a driving circuit is provided on the anisotropic conductive film. Then,the anisotropic conductive film is cured, wherein a bonding temperatureof the anisotropic conductive film is greater than or equal to 140° C.and less than or equal to 165° C.

These and other objectives of the present disclosure will no doubtbecome obvious to those of ordinary skill in the art after reading thefollowing detailed description of the embodiment that is illustrated inthe various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically illustrates a top view of a flexible substrate anda bonding structure according to an embodiment of the presentdisclosure;

FIG. 1B schematically illustrates a cross sectional view along asectional line A-A′ of FIG. 1A;

FIG. 1C schematically illustrates a cross sectional view of the flexiblesubstrate and the bonding structure corresponding to the sectional lineA-A′ of FIG. 1A according to some embodiments of the present disclosure;

FIG. 2 schematically illustrates a cross sectional view of the bondingstructure provided with an anisotropic conductive film;

FIG. 3A and FIG. 3B schematically illustrate a cross sectional view ofthe anisotropic conductive film being cured and a cross sectional viewof a driving circuit provided on the anisotropic conductive film,respectively;

FIG. 4 schematically illustrates a cross sectional view of a thin filmtransistor and a pixel electrode according to some embodiments of thepresent disclosure;

FIG. 5A schematically illustrates a top view of a flexible displaydevice according to an embodiment of the present disclosure; and

FIG. 5B illustrates a cross sectional view along a sectional line B-B′of FIG. 5A.

DETAILED DESCRIPTION

The present disclosure may be understood by reference to the followingdetailed description, taken in conjunction with the figures as describedbelow. It is noted that, for purposes of illustrative clarity and beingeasily understood by the readers, various figures of this disclosure maymerely show a portion of a flexible display device, and certain elementswithin may not be drawn to scale. In addition, the number and dimensionof each element shown in the figures are illustrative and are notintended to limit the scope of the present disclosure.

Certain terms are used throughout the description and following claimsto refer to particular elements. As one skilled in the art willunderstand, electronic equipment manufacturers may refer to an elementby different names. This document does not intend to distinguish betweenelements that differ in name but not in function. In the followingdescription and in the claims, the terms “include”, “comprise” and“have” are used in an open-ended fashion, and thus should be interpretedto mean “include, but not limited to . . . ”.

It should be understood that, when an element or a layer is “disposedon” or “connected to” another element or layer, it may be directlyconnected to the another element or layer, or other elements or layersmay be inserted therebetween (indirect conditions). Conversely, when anelement is “directly connected to” or “directly disposed on” anotherelement or layer, no other elements or layers are inserted therebetween.

Although terms such as first, second, etc. may be used in thedescription and following claims to describe various elements in claims,these terms do not mean or represent the claimed elements follow certainorder and do not represent the order of one claimed element and anotherclaimed element, or their manufacturing sequence. These terms are usedto discriminate a claimed element with a denomination from anotherclaimed element with the same denomination.

It should be noted that the technical features in different embodimentsdescribed in the following description may be replaced, recombined, ormixed with one another to constitute another embodiment withoutdeparting from or conflicting with the spirit of the present disclosure.

The electronic device of the present disclosure may include a displaydevice, an antenna device, a sensing device, a light-emitting device, ora tiled device but not limited thereto. The electronic device mayinclude a bendable or flexible electronic device. The electronic devicemay for example include liquid crystal materials, light-emitting diodes,fluorescent materials, phosphors, other suitable materials, orcombinations of the aforementioned materials or devices and not limitedthereto. The light-emitting diode may for example include an organiclight-emitting diode (OLED), a sub-millimeter sized light-emitting diode(mini LED), a micrometer-sized light-emitting diode (micro LED), aquantum dot light-emitting diode (quantum dot LED, QLED, or QDLED), anano-wire light-emitting diode (nano-wire LED) or a bar-typelight-emitting diode. The description below uses a display device as anexample of the electronic device to illustrate features of the presentdisclosure, but the present disclosure is not limited thereto.

FIG. 1A to FIG. 3B schematically illustrate a method for manufacturing aflexible display device according to an embodiment of the presentdisclosure, wherein FIG. 1A schematically illustrates a top view of aflexible substrate and a bonding structure according to an embodiment ofthe present disclosure, FIG. 1B schematically illustrates a crosssectional view taken along a sectional line A-A′ of FIG. 1A, FIG. 2schematically illustrates a cross sectional view of an anisotropicconductive film provided on the bonding structure, FIG. 3A and FIG. 3Bschematically illustrate a cross sectional view of the anisotropicconductive film being cured and a cross sectional view of a drivingcircuit provided on the anisotropic conductive film, respectively. Themethod for manufacturing the flexible display device will be describedin detail in conjunction with FIG. 1A to FIG. 3B. As shown in FIG. 1Aand FIG. 1B, first, a flexible substrate 10 and a bonding structure 12are provided, wherein the bonding structure 12 is disposed on theflexible substrate 10. In this step, the flexible substrate 10 and thebonding structure 12 may be disposed on a carrier (such as a carrier 36shown in FIG. 3A) or other suitable supporting platforms for performingsubsequent processes. The flexible substrate 10 may be a substrate forthe flexible display device, so that the flexible display device may bebendable. Material of the flexible substrate 10 may for example includepolyimide (PI), polyethylene terephthalate (PET), polycarbonate (PC),polyether sulfone (PES), polybutylene terephthalate (PBT), polyethylenenaphthalate (PEN), polyarylate (PAR), other suitable materials, or acombination thereof, but not limited thereto. In the embodiment shown inFIG. 1A, the quantity of the bonding structure 12 may be plural, but thequantity is not limited to those shown in the figure. In someembodiments, the quantity of the bonding structure 12 may be at leastone.

To clearly describe the method of the present disclosure, the followingcontents use single bonding structure 12 as an illustrative example, butthe quantity of the bonding structure 12 is not limited thereto. Asshown in FIG. 1B, the bonding structure 12 includes a plurality oflayers, in which these layers may include a conductive bonding pad 121,a first bonding pad 122 and an insulating layer 123. The conductivebonding pad 121 is disposed between the first bonding pad 122 and theflexible substrate 10, and the insulating layer 123 is disposed betweenthe conductive bonding pad 121 and the first bonding pad 122. Theinsulating layer 123 may be a single-layer structure or a multilayerstructure. When a flexible display panel 1 is a fringe-field switching(FFS) liquid crystal display panel, the layers of at least one of thebonding structures 12 may further include a second bonding pad 124disposed on the first bonding pad 122, so that the second bonding pad124 may be electrically connected to the conductive bonding pad 121 viathe first bonding pad 122. For example, the layers of the bondingstructure 12 may further include an insulating layer 125 disposedbetween the second bonding pad 124 and the first bonding pad 122, andalong a top-view direction VD, the insulating layer 125 may have atleast one opening 125 a overlapping with the second bonding pad 124 andthe first bonding pad 122, such that the second bonding pad 124 may beelectrically connected to the first bonding pad 122 through the opening125 a, thereby being further connected to the conductive bonding pad 121electrically. In some embodiments, when the insulating layer 123 is amultilayer structure, the insulating layer 123 may for example includeinsulating layers 126, 127 disposed between the conductive bonding pad121 and the first bonding pad 122. The insulating layer 126 may have atleast one opening 126 a, and the insulating layer 127 may have at leastone opening 127 a. In some embodiments, the opening 125 a may overlapwith the opening 126 a and the opening 127 a along the top-viewdirection VD. In some embodiments, the opening 125 a may overlap withthe opening 127 a but not the opening 126 a along the top-view directionVD. In some embodiments, the opening 125 a may not overlap with both theopening 126 a and the opening 127 a along the top-view direction VD, butnot limited thereto.

Please refer to FIG. 1C, which schematically illustrates a crosssectional view of the flexible substrate and the bonding structurecorresponding to the sectional line A-A′ of FIG. 1A according to someembodiments of the present disclosure. In some embodiments, the bondingstructure 12 may not include the second bonding pad 124 and theinsulating layer 125. In some embodiments, the insulating layer 123 maybe a single-layer structure with at least one opening 123 a, such thatthe first bonding pad 122 may be electrically connected to theconductive bonding pad 121 through the opening 123 a. The quantity ofthe opening 123 a may be single or plural. For example, the opening 123a may overlap with the conductive bonding pad 121 and the first bondingpad 122 along the top-view direction VD of the flexible substrate 10.

The conductive bonding pad 121, the first bonding pad 122 and the secondbonding pad 124 may include transparent conductive materials such asindium tin oxide (ITO), indium zinc oxide (IZO), other suitablematerials or a combination thereof, and/or they may include metals suchas aluminum, copper, titanium, molybdenum nitride, other suitablematerials or a combination thereof, but not limited thereto. Theinsulating layer 123, the insulating layer 125, the insulating layer126, and the insulating layer 127 may include inorganic insulatingmaterials, such as silicon nitride, silicon oxide, other suitablematerials, or a combination thereof; they may also include organicinsulating materials, such as polyfluoroalkoxy (PFA),polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), othersuitable materials, or a combination thereof. In the present disclosure,the “bonding structure” used herein may be defined as the conductivebonding pad 121 and a portion on the conductive bonding pad 121 in thestep of providing the bonding structure 12. For example, in theembodiment shown in FIG. 1B, the first bonding pad 122, the secondbonding pad 124, the insulating layer 125, the insulating layer 126, andthe insulating layer 127 on the conductive bonding pad 121 in thetop-view direction VD may be the bonding structure 12; in an embodimentshown in FIG. 1C, the first bonding pad 122 and the insulating layer 123on the conductive bonding pad 121 in the top-view direction VD may bethe bonding structure 12, but not limited thereto.

In some embodiments, a shape of the bonding structure 12 in the top-viewdirection VD may for example be rectangular, and a length of the bondingstructure 12 in a direction D1 is greater than a length of the bondingstructure 12 in a direction D2 perpendicular to the direction D1, butnot limited thereto. In some embodiments, the bonding structure 12 mayhave other geometric shapes or curved edges, but not limited thereto.

In some embodiments, as shown in FIG. 1A and FIG. 1B, the step ofproviding the bonding structure 12 may further include providingconductive lines 14. The conductive lines 14 may for example extendalong the direction D1 and be electrically connected to the conductivebonding pad 121 of the corresponding bonding structures 12 respectively.In some embodiments, the conductive lines 14 may be alternately arrangedin the direction D2, and the bonding structures 12 respectivelyconnected to two adjacent conductive lines 14 may have a staggeredarrangement in the direction D2. In some embodiments, the conductivelines 14 and the conductive bonding pad 121 may include transparentconductive materials, such as indium tin oxide (ITO), indium zinc oxide(IZO), other suitable materials or a combination thereof; they may alsoinclude metals, such as aluminum, copper, titanium, molybdenum nitride,other suitable materials or a combination thereof, but not limitedthereto. For example, the conductive lines 14 and the conductive bondingpad 121 may be formed of the same layer of material, but not limitedthereto.

Please refer to FIG. 4, which schematically illustrates a crosssectional view of a thin film transistor and a pixel electrode accordingto some embodiments of the present disclosure. In some embodiments, thestep of providing the flexible substrate 10 and the bonding structure 12may further include providing a plurality of thin film transistors 16 onthe flexible substrate 10. For the sake of clarity, FIG. 4 illustrates asingle thin film transistor, but not limited thereto. As shown in FIG.1A and FIG. 4, the flexible display panel 1 may include the flexiblesubstrate 10, the bonding structure 12 and the thin film transistor 16.In this configuration, the flexible display panel 1 may have a displayregion DR for displaying images and a peripheral region PR for disposingperipheral circuits, and the thin film transistor 16 may be disposedwithin the display region DR, while the bonding structure 12 may bedisposed within the peripheral region PR. The thin film transistor 16within the display region DR may be used for controlling or driving apixel or sub-pixel of the flexible display panel 1 to display. In someembodiments, the flexible display panel 1 may also include other thinfilm transistors disposed within the peripheral region PR.

In some embodiments, as shown in FIG. 4, the thin film transistor 16includes a plurality of film layers that include a gate 161, a gateinsulating layer 162, a semiconductor layer 163, and source/drains 164,165. Taking a bottom-gate type thin film transistor 16 as anillustrative example, the gate 161 is disposed on the flexible substrate10; the gate insulating layer 162 is disposed on the gate 161 and theflexible substrate 10; the semiconductor layer 163 is disposed on thegate insulating layer 162 and overlaps with the gate 161 in the top-viewdirection VD; and the source/drains 164, 165 are disposed on thesemiconductor layer 163 and respectively on opposite sides of the gate161 in the top-view direction VD, but not limited thereto. In someembodiments, the gate 161 and the conductive bonding pad 121 of thebonding structure 12 includes the same materials, such as aluminum,molybdenum nitride, copper, titanium, other suitable materials, or acombination thereof. For example, the gate 161 and the conductivebonding pad 121 may be formed of the same metal layer, wherein the metallayer may be a single-layer structure or a multilayer structure.

Depending on the type of the thin film transistor 16, the gate 161, thegate insulating layer 162, the semiconductor layer 163 and thesource/drains 164, 165 may also have different configurations. The thinfilm transistor 16 may for example be a top-gate type transistor, or,depending on demands, be altered to a double-gate type or dual-gate typetransistor or other suitable transistors. Alternatively, the thin filmtransistor 16 may for example include an amorphous silicon (a-Si)transistor, a low-temperature poly-silicon (LTPS) transistor, ametal-oxide semiconductor (such as indium gallium zinc oxide, IGZO)transistor, but not limited thereto.

In some embodiments, the flexible display panel 1 may further include aplanarizing layer 18 disposed on the thin film transistor 16. In someembodiments, the flexible display panel 1 may further include a pixelelectrode 20 disposed on the planarizing layer 18; in such situation,the planarizing layer 18 may have one opening 18 a, and the pixelelectrode 20 is electrically connected to one of the source/drains 164,165 of the corresponding thin film transistor 16 through the opening 18a. In some embodiments, the pixel electrode 20 may include transparentconductive materials, such as indium tin oxide, indium zinc oxide, othersuitable materials or a combination thereof. In some embodiments,depending on the type of the flexible display panel 1, the flexibledisplay panel 1 may further include other elements used for displayingimages. For example, the flexible display panel 1 may be anon-self-luminous display panel. Taking a liquid crystal display panelas an illustrative example of the flexible display panel 1, the flexibledisplay panel 1 may further include another flexible substrate (such asthe flexible substrate 22 shown in FIG. 3A) and a liquid crystal layer(such as the liquid crystal layer 24 shown in FIG. 3A), wherein twoflexible substrates are disposed opposite to each other and bonded toeach other through a sealant (such as a sealant 26 shown in FIG. 3A, andthe liquid crystal layer is disposed between the two flexible substrates10, 22; in such situation, the another flexible substrate does not coverthe bonding structure 12. In some embodiments, when the flexible displaypanel 1 is the FFS liquid crystal display panel, the flexible displaypanel 1 may further include a common electrode (not illustrated)disposed on the planarizing layer 18 to generate an in-plane electricfield with the pixel electrode 20. In some embodiments, the flexibledisplay panel 1 may also be a self-luminous display panel that mayinclude light-emitting elements (not illustrated) disposed on thecorresponding pixel electrode 20 and electrically connected to thecorresponding pixel electrode 20. The light-emitting element may forexample include OLEDs, mini LEDs, micro LEDs, QLEDs or QDLEDs. Materialof the another flexible substrate may for example include PI, PET, PC,PES, PBT, PEN, PAR, other suitable materials, or a combination thereof,but not limited thereto.

In some embodiments, at least one film layer of the thin film transistor16 may include the same material as a film layer of at least one bondingstructure 12 and be formed by the same manufacturing process as the filmlayer of at least one bonding structure 12. In some embodiments, aportion of the thin film transistor 16 may include the same material asa portion of at least one bonding structure 12 and be formed by the samemanufacturing process as the portion of at least one bonding structure12. For example, in some embodiments, the gate 161 of the thin filmtransistor 16 and the conductive bonding pad 121 of the bondingstructure 12 may include the same material. In some embodiments, thegate insulating layer 162 of the thin film transistor 16 and theinsulating layer 126 of the bonding structure 12 may include the samematerial. In some embodiments, the pixel electrode 20 may include thesame material as the first bonding pad 122 or the second bonding pad124; for example, the pixel electrode 20 is formed of the sametransparent conductive layer as the first bonding pad 122 or the secondbonding pad 124. In some embodiments, when the flexible display panel 1is the FFS liquid crystal display panel, the pixel electrode 20 and oneof the first bonding pad 122 and the second bonding pad 124 may beformed of the same transparent conductive layer, and the commonelectrode and the other one of the first bonding pad 122 and the secondbonding pad 124 may be formed of another transparent conductive layer.In some embodiments, the planarizing layer 18 may be the same insulatinglayer as one of the insulating layer 125 and the insulating layer 127.In some embodiments, one of film layers of the thin film transistor 16and the corresponding film layer of the bonding structure 12 may beformed of the same material by different manufacturing processes orformed of different materials by different manufacturing processes.

As shown in FIG. 2, after the step of providing the flexible substrate10 and the bonding structure 12 is completed, an anisotropic conductivefilm 28 is provided on the bonding structure 12. For example, theanisotropic conductive film 28 may include an insulating adhesive resinand a plurality of conductive particles disposed within the insulatingadhesive resin (such as conductive particles 28 a shown in FIG. 5B), butnot limited thereto.

As shown in FIG. 3A and FIG. 3B, after the step of providing theanisotropic conductive film 28 is completed, a driving circuit 30 isprovided on the anisotropic conductive film 28; subsequently, theanisotropic conductive film 28 is cured at a bonding temperature greaterthan or equal to 140° C. and less than or equal to 165° C., so that thedriving circuit 30 is bonded and electrically connected to the bondingstructure 12 through the anisotropic conductive film 28. In this step ofcuring the anisotropic conductive film 28, the anisotropic conductivefilm 28 reaches the same or similar temperature as the flexiblesubstrate 10. In this manner, a flexible display device 100 may beproduced. In some embodiments, the step of providing the driving circuit30 includes disposing the driving circuit 30 on the anisotropicconductive film 28, and making the driving circuit 30 contact theanisotropic conductive film 28; then, the step of curing the anisotropicconductive film 28 may be performed through a top heating structure 32disposed on the driving circuit 30 and a bottom heating structure 34disposed under the flexible substrate 10, so as to perform thermalcuring on the anisotropic conductive film 28. For example, the topheating structure 32 and the bottom heating structure 34 may bepreheated; then, by contacting the driving circuit 30 and the flexiblesubstrate 10, the anisotropic conductive film 28 may be thermally cured.In some embodiments, during the step of curing the anisotropicconductive film 28, the bonding temperature of the anisotropicconductive film 28 may also be greater than or equal to 150° C. and lessthan or equal to 160° C. In some embodiments, the flexible displaydevice 100 may include the flexible display panel 1, the anisotropicconductive film 28 and the driving circuit 30.

The driving circuit 30 may for example be an integrated circuit chip, aflexible printed circuit board or other suitable elements, wherein theflexible printed circuit board may include a chip-on-film (COF) typecircuit or other suitable types, but not limited thereto. The drivingcircuit 30 may for example include a plurality of bonding pads 30 a, andeach bonding pad 30 a may be bonded and electrically connected to thecorresponding bonding structure 12 respectively. In some embodiments,when the driving circuit 30 is the integrated circuit chip, atemperature of the top heating structure 32 may be greater than or equalto 195° C. and less than or equal to 205° C., and a temperature of thebottom heating structure 34 may be greater than or equal to 85° C. andless than or equal to 95° C., such that the bonding temperature of theanisotropic conductive film 28 may be within a range greater than orequal to 140° C. and less than or equal to 165° C. In some embodiments,when the driving circuit 30 is the flexible printed circuit board, thetemperature of the top heating structure 32 may be greater than or equalto 235° C. and less than or equal to 245° C., the temperature of thebottom heating structure 34 may be greater than or equal to 105° C. andless than or equal to 115° C., such that the bonding temperature of theanisotropic conductive film 28 may be within a range greater than orequal to 140° C. and less than or equal to 165° C. In some embodiments,during the step of curing the anisotropic conductive film 28, the topheating structure 32 and the bottom heating structure 34 may be pressedto the flexible substrate 10 and the driving circuit 30, therebyimproving the bonding therebetween.

It should be noted that, when the anisotropic conductive film 28 iscured at the bonding temperature greater than 165° C. (such as thebonding temperature of 170° C.), due to the large difference between thecoefficient of thermal expansion (CTE) of the flexible substrate 10 andother film layers, peeling may occur at an interface between the bondingpad (such as the first bonding pad 122 or the second bonding pad 124) ofthe produced flexible display device and the insulating layer (such asthe insulating layer 125 or the insulating layer 127) during reliabilitytesting. In the present disclosure, by means of curing the anisotropicconductive film 28 at a bonding temperature greater than or equal to140° C. and less than or equal to 165° C., peeling at the interfacebetween the second bonding pad 124 and the insulating layer 125, theinterface between the first bonding pad 122 and the insulating layer125, or the interface between the first bonding pad 122 and theinsulating layer 127 during reliability testing may be reduced oravoided, thereby improving the quality of the electrical connectionbetween the driving circuit 30 and the bonding structure 12. In thismanner, the display quality or reliability of the flexible displaydevice 100 may be improved.

In the section below, a structure of the flexible display device formedby the aforementioned manufacturing method will be further described indetail. Please refer to FIG. 5A and FIG. 5B. FIG. 5A schematicallyillustrates a top view of a flexible display device according to anembodiment of the present disclosure, and FIG. 5B illustrates a crosssectional view taken along a sectional line B-B′ of FIG. 5A. Forclarity, FIG. 5B omits detailed film structures of the bondingstructure, but the present disclosure is not limited thereto. As shownin FIG. 5A and FIG. 5B, a flexible display device 200 may include theflexible substrate 10, at least one bonding structure group 38, thedriving circuit 30 and the anisotropic conductive film 28, wherein thebonding structure group 38 may include a plurality of bonding structures12 arranged side-by-side. A quantity of the bonding structures 12forming the bonding structure group 38 may be modified depending on adesign or requirement of the corresponding driving circuit 30electrically connected thereto. For example, the bonding structure group38 may be consisted of seven bonding structures 12, and thecorresponding driving circuit 30 that electrically connected to thebonding structure group 38 has seven bonding pads 30 a, but not limitedthereto. The flexible substrate 10, the bonding structure 12, thedriving circuit 30 and the anisotropic conductive film 28 of the presentembodiment may be structured as FIG. 3B and will not be repeated. Insome embodiments, the flexible display device 200 may be identical tothe structure shown in FIG. 3A which further includes another flexiblesubstrate 22, the liquid crystal layer 24 and a seal 26, but not limitedthereto.

In the present embodiment, the bonding structure group 38 has a firstwidth W1 in the direction D2, and one of the bonding pads 30 a of thedriving circuit 30 has a second width W2 in the direction D2. If theflexible substrate 10 of the flexible display device 200 deforms due totemperature fluctuation, the bonding structure group 38 of the flexiblesubstrate 10 may also experience change in width. If an overall width ofthe bonding structure group 38 changes too drastically, it is possiblethat at least one bonding structure 12 of the bonding structure group 38may not be electrically connected to the bonding pad 30 a of the drivingcircuit 30, thereby affecting normal operations of the flexible displaydevice 200. In order for the driving circuit 30 to be electricallyconnected to the bonding structures 12 of the bonding structure group38, the first width W1 and the second width W2 need to satisfy thefollowing expression: (140−Trt)×CTE×W1<W2, where the value 140 is thetemperature of the anisotropic conductive film 28 and the flexiblesubstrate 10 reached during curing of the anisotropic conductive film28, Trt is room temperature with a unit in degrees Celsius (° C.), CTEis a coefficient of thermal expansion of the flexible substrate 10 witha unit of 10⁻⁶/° C., W1 is the first width, W2 is the second width, andunits of W1 and W2 are micrometers. In some embodiments, a bondingtemperature Tacf to cure the anisotropic conductive film 28 satisfiesthe following relationship: 140° C. Tacf 165° C. Room temperature mayfor example be 25° C. or from 15° C. to 30° C., but not limited thereto.The “first width W1” of the bonding structure group 38 of the presentdisclosure may be defined as a maximum width between exterior edges ofthe two outermost bonding structures 12 of the bonding structure group38 arranged in the direction D2; for example, in the bonding structuregroup 38 shown in FIG. 5B, the first width W1 may be the maximum widthbetween the left edge of the left most bonding structure 12 and theright edge of the right most bonding structure 12. The “second width W2”of the bonding structure group 38 of the present disclosure may bedefined as a maximum width between two edges of single bonding structure12 arranged in the direction D2.

It should be noted that, when curing the anisotropic conductive film 28,because the coefficient of thermal expansion of the flexible substrate10 is greater than that of the other film layers of the flexible displaydevice 200 (such as the insulating layer, the conductive bonding pad orthe bonding pad of the bonding structure 12), a distance betweenadjacent bonding structures 12 on the flexible substrates 10 increaseswith increasing temperature. The increase in the first width W1 of thebonding structure group 38 as temperature increases is a sum of thechanges of the distances between adjacent bonding structures 12 of thebonding structure group resulting from the change in temperature. Theanisotropic conductive film 28 and the flexible substrate 10 may reachthe same temperature during curing of the anisotropic conductive film28; therefore, when the flexible substrate 10 is heated from roomtemperature to the bonding temperature of the anisotropic conductivefilm 28, the first width W1 of the bonding structure group 38 may changedue to thermal expansion of the flexible substrate 10. As a result, thechange in the first width W1 of the bonding structure group 38 may beexpressed as (Tacf−Trt)×CTE×W1. In order for the driving circuit 30 andthe bonding structures 12 of the bonding structure group 38 to beelectrically connected to each other, the change in the first width W1of the bonding structure group 38 needs to be less than the second widthW2 of single bonding pad 30 a of the driving circuit 30, so that duringcuring of the anisotropic conductive film 28, each bonding structure 12of the bonding structure group 38 in the top-view direction VD may stilloverlap with the corresponding bonding pad 30 a respectively, and thatinadequate bonding between the bonding structure 12 and thecorresponding bonding pad 30 a may be reduced.

For example, when the flexible display device 200 is a liquid crystaldisplay device, the flexible substrate 10 may include transparent PIwith a CTE of about 38 ppm/° C. Or, when the flexible display device 200is an OLED display device, the flexible substrate 10 may include yellowPI with a CTE of about 6.4 ppm/° C. Therefore, relationships between thefirst width W1 and the second width W2 corresponding to different typesof the flexible display device 200 may be derived from the aboveexpression, leading to a design of the flexible display device 200 withreduced inadequate bonding issues.

For clarity, FIG. 5A uses a dotted frame to represent the bondingstructure group 38, and the bonding structure group 38 may beillustrated as shown in FIG. 5B, but not limited thereto. In someembodiments, the flexible display device 200 may include at least onebonding structure group 38 corresponding to the same driving circuit 30.For example, as shown in the embodiment of FIG. 5A, the flexible displaydevice 200 may also include a plurality of bonding structure groups 38.It should be noted that, two adjacent bonding structure groups 38 do nothave other bonding structures 12 between them, but the configuration isnot limited thereto. The plurality of bonding structure groups 38 may bebonded to different driving circuits 30 respectively. For example, thedriving circuit 30 may correspond to a gate driving circuit, a sourcedriving circuit or driving circuits with other functions, but notlimited thereto. In some embodiments, different driving circuits 30 mayalso be different portions of the same circuit board, but not limitedthereto.

In summary, in the method for manufacturing the flexible display deviceof the present disclosure, because the anisotropic conductive film iscured at the bonding temperature greater than or equal to 140° C. andless than or equal to 165° C., peeling at the interface between thebonding pad and the insulating layer during reliability testing may bereduced, thereby improving the display quality or reliability of theflexible display device. In the flexible display device of the presentdisclosure, because the flexible display device satisfies theexpression: Tacf<(W2/(CTE×W1))+Trt, during curing of the anisotropicconductive film, each bonding structure of the bonding structure groupin the top-view direction may overlap with the corresponding bondingpad, thereby may reduce the occurrence of inadequate bonding between thebonding structure and the corresponding bonding pad.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the disclosure. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for manufacturing a flexible displaydevice, comprising: providing a flexible substrate and a bondingstructure, wherein the bonding structure is disposed on the flexiblesubstrate; providing an anisotropic conductive film on the bondingstructure; providing a driving circuit on the anisotropic conductivefilm; and curing the anisotropic conductive film; wherein a bondingtemperature of the anisotropic conductive film is greater than or equalto 140° C. and less than or equal to 165° C.
 2. The method of claim 1,wherein the bonding temperature of the anisotropic conductive film isgreater than or equal to 150° C. and less than or equal to 160° C. 3.The method of claim 1, further comprising providing a plurality of thinfilm transistors on the flexible substrate.
 4. The method of claim 3,wherein a portion of one of the plurality of thin film transistors and aportion of the bonding structure are formed by a same process.
 5. Themethod of claim 1, wherein the anisotropic conductive film is cured by atop heating structure disposed on the driving circuit and a bottomheating structure disposed under the flexible substrate.
 6. The methodof claim 5, wherein the driving circuit is an integrated circuit chip.7. The method of claim 6, wherein a temperature of the top heatingstructure is greater than or equal to 195° C. and less than or equal to205° C.
 8. The method of claim 7, wherein a temperature of the bottomheating structure is greater than or equal to 85° C. and less than orequal to 95° C.
 9. The method of claim 5, wherein the driving circuit isa flexible printed circuit board.
 10. The method of claim 9, wherein atemperature of the top heating structure is greater than or equal to235° C. and less than or equal to 245° C.
 11. The method of claim 10,wherein a temperature of the bottom heating structure is greater than orequal to 105° C. and less than or equal to 115° C.